1. Field of the Invention
This invention relates to an optical scanner and particularly to an optical scanner which has the required control circuit built in an interface card connectable with an interface connector located in a motherboard of a computer.
2. Description of the Prior Art
A conventional flatbed optical scanner 1 like the one shown in FIG. 1 generally includes a casing 11, a scanning means 12, a control circuit board 14 located in the casing 11 and a power supply 5. A scanning document 3 is placed on a transparent glass 16 and covered by a cover 17. The scanning means 12 is moved to and fro by means of a motor 18 and a transmission means 13 along a guide rod 134 to scan the document 3. The data and image being scanned is converted to computer acceptable format by the control circuit board 14 and fed to a parallel port 24 of the computer 2 through a cable 25. The power needed in the scanner is provided by a DC power supply 5 (DC transformer) to the control circuit board 14 which further wires respectively to the scanning means 12 and the motor 18 via a signal line 141 and a power line 142 for controlling the motion of the scanning means 12 and the motor 18. The transmission means 13 usually includes a reducing gear 131, a belt 132 or steel cable and a plural number of rollers 133. In the construction set forth above, the control circuit board 14 is located in the casing 11, and an extra power supply 5 provides the power needed. It has the following drawbacks:
1. It is difficult to shrink the size of the scanner. As the scanning means 12 has to move a full range to completely cover the document 3 edge to edge, the width and length of the scanner 1 has certain minimum limitation, e.g., should be larger than an A4 size paper. In order to make the scanner smaller size to fit other equipment such as a computer, the height of the scanner becomes the only variable attackable. The scanning means 12, transmission means 13 and guide rod 134 have some physical working requirements. The control circuit board 14 and its protection shield 15 located thereabove usually take 10-20% of the height of the casing 11. Furthermore the casing 11 usually has connector sockets reserved for other purpose, such as a power socket 191 for connecting with the power supply 5, a printer socket 192 for a printer 4 and a CPU socket 193 for connecting to the computer 2. All this making it difficult to cut the height of a conventional scanner.
2. Limitation of transmission interface.
Conventional scanner transmits capturing data and image to the computer through a parallel port which is generally a low speed interface and consequently drags down overall scanning efficiency. Furthermore a personal computer generally has only one parallel port. If a user wants to connect a printer and a scanner to the computer at the same time, these two devices have to connect in series to the same parallel port. It creates a lot of usage inconvenience.
3. Difficult to cut cost.
As mentioned before, with the control circuit board 14 located in the casing 11, total height of the casing 11 will increase 10-20%. Package materials, storage space and cost, and transportation cost will also increase by 10-20%. Power supply 5 will become another extra cost. Not only the cost of the power supply 5 itself may become extra cost of the scanner, but also the power supply 5 will add even more weight and size. In addition, when a user wants to use a notebook computer outdoors without a power socket, the scanner cannot be connected or functioned.
4. High electromagnetic interference (EMI)
Most conventional scanners has plastic casing 11 which has poor EMI protection. The control circuit board 14 will generate electromagnetic wave during scanning operation and will result in EMI to other electronic devices or even human bodies located nearby.